A basic sheet fed printer feed tray, as shown in FIG. 1, has an angled front plate 1 and a positionally adjustable angled rear plate 2 between which rests a stack 3 of printable material such as paper, vinyl, polyester and the like. The angle of rear plate 2 is slightly less than the angle of front plate 1 so that, when the stack of paper 3 is properly placed in the feed tray so that its rear edge rests against rear plate 2, a small gap 4 exists between the leading edge of the paper 3 and the front plate 1. The top sheet of the stack of paper 3 is urged into the paper path 5 by rollers 6 (only one of which is shown) which are biased toward the paper stack 3 and which drive the top sheet of paper stack 3 onto the ramp of front plate 1 where it is directed into paper path 5. Although there is a space provided by gap 4 into which the top sheet of the paper 3 could downwardly extend and thereby fail to be directed into paper path 5, this very rarely occurs because gap 4 is quite small. However, the size of the gap 4 is dramatically increased, and jamming problems and/or damage to the leading edge of the paper or other media frequently occur, when a common feed tray as described hereinabove is used to feed paper having variable thickness along its length.
The present invention deals generally with the problem encountered when feed trays are used to feed paper of variable thickness. More specifically, the invention deals with the problems encountered when feed trays are used to feed dual web forms to a printer. A type of dual web form, as now known in the art, is depicted in FIG. 2. Such dual web forms are sheets of variable thickness having a thicker, pressure sensitive adhesive portion 7 separated by perforations 8 from a thinner paper portion 9. A face paper 10 is separated along its length by perforations 8. On one side of the perforation 8, the face paper 7 contains a pressure sensitive adhesive 11 which is releasably adhered to a silicone release layer 12 carried on a backing sheet 13.
An exemplary common use for these dual web forms is the creation of labels for prescription medication. By properly configuring a printer and associated program, a pharmacist can have prescription information printed on a label on the pressure sensitive adhesive portion 7 of the dual web form and, at the same time, can have the same or related information printed on the paper portion 9. The labels, now bearing the prescription information, can be removed from the backing sheet 13 bearing the silicone release layer 12 and applied to a patient's bottle of prescription medication, while the prescription information printed on the paper portion 9 of the dual web form can be separated from the label portion by tearing along the perforation 8 and can then be placed in the pharmacist's files and/or be given to the patient. However, the use of dual web forms with a printer having a common feed tray tends to jam the printer.
A jamming problem arises with the use of dual web forms due to the fact that the pressure sensitive adhesive portion 7 of the dual web form is thicker than the paper portion 9. Dual web forms are stacked in a feed tray with the thicker, pressure sensitive adhesive portion 7 directed toward the ramped front plate 1 and, as can be seen in FIG. 3, the variable thickness of the dual form causes a significant increase in the size of the gap 4 when a stack of dual web forms are placed in the feed tray. When the rollers 6 attempt to feed the top dual web form into the paper path 5, the leading edge of the dual web form has a greater tendency to feed downwardly into the large gap 4 and jam the printer as at 15. This problem is especially apparent when individual forms in the stack of dual web forms in the feed tray happen to have a slight downward curve at their leading edge. This downward curve may result from an inherent curl characteristic of many laminates as a result of ambient humidity conditions, or it may result from mechanical deformation of the laminate. Moreover, the size of the gap 4 is such that quickly closing a feed tray or accidentally jostling the tray around may cause the top dual web forms on the stack to shift and extend into the gap 4 thereby creating a jamming situation before feeding from the paper stack 3 has even been attempted. The size of the gap 4 will depend upon the variation in thickness along the form's length as well as the overall thickness of the stack placed in the feed tray. Generally, the size of the gap with such dual web forms can range from about 0.25 to about 0.5 inches, with the larger gaps tending to result in jams more often. It has been found that the gap 4 is generally doubled when dual web forms are used, as compared to sheets of uniform thickness.
Therefore, there exists a need in the art for a feed device for printer feed trays that will prevent stacks of paper or other sheet material or other sheet material of variable thickness from jamming the printer.